Electric glow discharge device with telescoped electrodes



- May 5, 1970 TVC. E.II='OULKE ELECTRIC GLOW DISCHARGE DEVICE WITHTELESCOPE-1D ELECTRODES Filed Aug. 2. 1967 lnvervtor: Ted E. Foutke b91s A how-neg United States Patent US. Cl. 313210 9 Claims ABSTRACT OFTHE DISCLOSURE A crater-type electric glow discharge device having anenvelope containing a rare gas and comprised of a pair of coldelectrodes consisting of telescoped outer and inner metal tubes with aglass seal hermetically joining the inner electrode tube to one end ofthe outer electrode tube and supporting them in spaced concentricrelation with the inner tube terminating short of a glass windowhermetically sealing oif the other end of the outer electrode tube. Theouter end of the inner electrode tube is also hermetically sealed 01f.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates in general to gaseous electric discharge devices and moreparticularly to such devices of the cathode or negative glow type.

Description of the prior art Glow lamps, as generally known in the art,usually comprise a sealed envelope containing one or more rare gasessuch as neon or argon at a suitable pressure and, in some cases, fordark adaptation of the device,,also containing a radioactive element tofacilitate rapid response in starting of the discharge. Within theenvelope, and properly spaced from each other, an anode and a cathodeare so disposed that a comparatively low voltage applied thereacrosswill produce a discharge within the envelope causing the cathode tobecome enveloped in a glow.

Where it is desired to obtain a very concentrated light source in suchglow lamps, the cathode or negative electrode thereof is formed with acavity or deep recess and the gas pressure is so chosen with relation tothe dimensions of the recess and the voltage of the supply circuit thatsubstantially all the discharge occurs in the recess or crater in theelectrode, thereby producing a spot of intense light or glow the size ofthe cross section of the recess, and variable in luminosity withvariations of current in the supply circuit. Such crater-type glow lampsare useful as a light source in apparatus for transmitting facsimiles,photographs and motion pictures by wire or by radio, and as the lightsource of the receiver or reproducer in television apparatus and formany other purposes where a very concentrated light source is required.

The concentrated glow discharge produced by such crater-type glowdischarge lamps is also well adapted for use in lighting arrays orgroupings thereof to form an illuminated readout or other display devicesuch as, for example, a numeric or alpha-numeric readout device.However, in the prior crater-type glow discharge lamps, the lampelectrodes and associated supporting structures generally have beenmounted Within a separate enclosing envelope the additional size ofwhich therefore adds to the overall size of the lamp. As a result,lighting arrays composed of such prior crater-type glow discharge lampsmounted alongside one another are characterized by comparatively poordelineation and readability of the illumi- 3,510,717 Patented May 5,1970 nated characters produced by the lighting array owing to the factthat, because of the dimensional size of the lamp envelope, the craterglow discharges produced within the individual lamps making up thelighting array necessarily are spaced an inordinate distance apart. Thedimensional size of the enclosing envelopes of such prior crater-typeglow discharge devices also places a limitation on the minimum overallsize of lighting array which can be obtained therewith.

Summary of the invention It is an object of the invention, therefore, toprovide a crater-type glow discharge device of the end-on light emissiontype which is of appreciably smaller width dimension than that of priorcrater-type glow discharge devices.

Another object of the invention is to provide a cratertype glowdischarge device comprised of an enclosing envelope formed principallyby the cathode and anode electrodes of the device.

Still another object of the invention is to provide a crater-type glowdischarge device which is of simplified construction such as lendsitself to fabrication by a simplified manufacturing procedure.

A further object of the invention is to provide a cratertype glowdischarge device of the end-on light emission type which is of minimalwidth dimension such as permits the mounting of a large number of thedevices sideby-side in a relatively close space to thereby form alighting array readout capable of producing lighted characters ofgreatly improved delineation and readability as compared to thatobtained heretofore with prior type glow discharge devices.

Briefly stated, in accordance with one aspect of the invention, acrater-type glow discharge device is made of minimum width dimension orsize by having the envelope of the device formed principally by themetal cathode and anode electrodes thereof, for which purpose theelectrodes are constituted by telescoped inner and outer metal tubes theouter one of which is hermetically sealed at one end by a glass windowand at its other end to the inner electrode tube by a glass seal whichserves to support the electrode tubes in spaced concentric relation. Thedevice is evacuated, and filled with one or more rare gases at a lowpressure, through the outer end of the inner metal tube which is thenhermetically sealed off in a suitable manner.

According to a further aspect of the invention, the in ner end of theinner electrode tube or cathode is located adjacent the glass window ofthe device so that the glow discharge which forms within the hollowinterior or crater of the inner electrode tube will, in turn, becorrespondingly located adjacent the glass window of the device tothereby afford a good end-on lighted appearance to the device duringoperation.

According to a still further aspect of the invention, the outer side ofthat portion of the inner electrode tube or cathode extending into theouter electrode tube or anode from the glass seal therebetween is coatedwith an anti-glow material to thereby positively assure the confinementof the glow discharge to the hollow interior space or crater of theinner electrode tube.

Further objects and advantages of the invention will appear from thefollowing detailed description of species thereof and from theaccompanying drawing.

Brief description of the drawing In the drawing:

FIG. 1 is a sectional view of a gaseous electric glow discharge deviceaccording to the invention;

FIG. 2 is a fragmentary perspective view, partly in section, of the glowdischarge device shown in FIG. 1;

FIG. 3 is a fragmentary sectional view of the outer end of the innerelectrode tube of the glow discharge device according to the inventionillustrating a modified manner of hermetically sealing off the saidinner electrode tube, and

FIG. 4 is an elevational view showing a number of individual glowdischarge devices according to the invention arranged in side-by-siderelation to form a representative lighting array or readout device.

Description of the preferred embodiments Referring to the drawing, theglow discharge device according to the invention comprises an envelope 1containing a gaseous filling of a rare gas such as neon, argon, heliumor krypton, or mixtures thereof, at a relatively low pressure within therange of, for example from 20 to 100 torr., to give the desiredbreakdown potential for the device. The envelope 1 is comprised of innerand outer metal tubes 2 and 3 which constitute the cold cathodeelectrode and anode electrode, respectively, of the discharge device andare hermetically sealed together and supported in spaced concentricrelation by a glass collar 4 fusion-sealed to the inner electrode tube 2and to one end 5 of the outer electrode tube 3 to form a glass sealtherebetween. The glass collar or seal 4 is made of a suitable glass,preferably any of the low expansion heat-resisting glasses such as arecustomarily referred to as hard glasses and are commonly employed in thelamp art for glass-to-metal seals. The electrode tubes 2 and 3 may bemade of any suitable metal having a coefficient of expansionapproximately matching that of the glass of the seal 4 and which willwet and adhere thereto. A preferred material for the cold electrodes 2and 3 is an alloy of iron, nickel and cobalt such as, for example, thatcommercially known as Kovar and consisting essentially of, by weight,54% iron, 29% nickel and 17% cobalt. As shown, the outer metal tube oranode 3 has an inside diameter somewhat greater than, but less thantwice the outside diameter of the inner metal tube or cathode 2 so thatthe spacial distance between the walls of the telescoped portions of themetal tubes 2 and 3 is considerably smaller than the inside diameter ofthe inner metal tube 2. A very closely compacted arrangement of thetelescoped tubes 2 and 3, and thus an optimum minimal outside dimensionfor the glow discharge device is thereby afforded, among other things.

The other end 6 of the outer electrode tube 3 is hermetically sealed offby a glass window 7 through which is emitted the light from the glowdischarge which forms within the hollow interior of the inner electrodetube or cathode 2 during the operation of the glow discharge device. Theglass of which the window 7 is made may be similar to that employed forthe glass seal 4.

As shown, the inner electrode tube or cathode 2 preferably extends intothe outer metal tube 3 from the glass seal 4 therebetween to a pointadjacent the glass window 7 so as to locate its inner end 8, and thusthe glow discharge which forms therewithin during the operation of thedevice, as near as possible to the glass window 7, thereby affordingmaximum emission of the light from the glow discharge within the cathodetube 2. The outer end of the inner electrode tube or cathode 2 ishermetically sealed off in a suitable manner, as by means of thetippedoif residue or glass tip 9 of a glass exhaust tube which isfusion-sealed to the end of the inner electrode tube 2 and through whichthe gas filling is introduced into the envelope 1.

If desired, the inside wall of the inner electrode tube 2 may be coatedwith a suitable electron emissive material of low work function such asis commonly employed in glow discharge devices to reduce the operatingvoltage of the device. A suitable electron emissive material for suchpurpose may be barium oxide.

While there is a strong tendency for the glow discharge to concentratewithin the inner electrode tube 2 during the operation of the glowdischarge device, it is advisable to coat the outer side of that portionof the inner electrode tube 2 which extends into the outer tube from theglass seal 4 therebetween with a suitable anti-glow material, asindicated at 10, in order to thereby assure the confinement of the glowdischarge within the interior of the inner electrode tube 2 at all timesduring the operation of the device. Finely powdered aluminum ispreferably used for the anti-glow coating 10, since it has been found tobe extremely elfective for this purpose, but any other substance whichhas the like property of resisting the creeping of the cathode glowdischarge, such as insulating materials like aluminum oxide, may be usedif desired.

Instead of the inner electrode tube 2 being hermetically sealed off atits outer end by the glass exhaust tube tip 9, it may be sealed off by aplug 11 of a suitable fusible material filling the outer end of theinner electrode tube 2, as shown in FIG. 3. The sealing plug 11 may beformed of metal that will wet and adhere to the particular metalemployed for the inner electrode tube 2. Thus, where the inner electrodetube 2 is made of an alloy of iron, nickel and cobalt such as Kovar, thesealing plug 11 may be formed of brass, for example.

In the operation of the electric glow discharge device according to theinvention, when the anode 3 and cathode 2 are connected, respectively,to the positive and negative sides of a DC. power supply of sufficientpotential to cause the breakdown of the device, a negative glowdischarge is formed in, and is confined within the hollow interior orcrater of the inner electrode tube 2. The concentrated light source thusformed by this glow discharge within the inner electrode tube 2 is thendirected outwardly from the open inner end 8 thereof as a concentratedbeam of light which then passes out through the glass window 7 in theend of the outer electrode tube 3. Because of the concentrated characterof the light beam produced by the glow discharge device according to theinvention, it is therefore well suited for use as a signal or indicatorlight, or in a lighting array composed of a grouping of such glowdischarge devices mounted in side-by-side relation to form a numeric orother type readout device 12, as shown in FIG. 4. By selective operationof respective ones of the individual glow discharge devices making upsuch a lighting array or readout device 12, lighted numbers, letters orother characters of the desired selection may be made to appear at theviewing end of the readout device.

Since no enclosing envelope other than that formed by the tubularelectrodes 2, 3 themselves is necessary in the glow discharge deviceaccording to the invention, the discharge device therefore is of minimumwidth dimension or size, thus permitting the mounting of a large numberof the devices side-by-side in a relatively close space to form areadout device 12. Thus, the glow discharge device according to theinvention not only enables the formation of lighting array readouts 12of considerably smaller size than that heretofore obtainable with priortype glow discharge devices, but also, and more importantly, assuresgreatly improved delineation and readability of the lighted charactersproduced by such readout devices because of the closer positioning ofthe light beams from the individual discharge devices in the lightingarray 12.

By forming the envelope 1 of the glow discharge device essentially outof the cathode and anode electrode elements 2, 3 thereof, in the manneraccording to the invention, the number of component parts required toform the discharge device is thereby reduced, thus resulting in acrater-type glow discharge device which is of greatly simplifiedconstruction and reduced cost and which can be fabricated by asimplified manufacturing procedure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric glow discharge device comprising an envelope comprised ofa pair of cold electrodes consisting of outer and inner metal tubestelescoped with one another, the outer electrode tube having a straightcylindrical inner wall of uniform diameter throughout its entire lengthand spaced from the inner electrode tube, said outer electrode tubehaving an inside diameter less than twice the outside diameter of theinner electrode tube and the inner electrode tube extending into theouter electrode tube from one end thereof but terminating short of itsother end, a glass seal hermetically joining the said one end of theouter electrode tube to the inner electrode tube and supporting them inspaced concentric relation, a glass window hermetically sealing off thesaid other end of the outer electrode tube, said inner electrode tubebeing hermetically sealed off at its outer end, and a filling of a raregas in said envelope at a low pressure.

2. An electric glow discharge device as specified in claim 1 wherein theinner end of the said inner electrode tube is located adjacent the saidglass window.

3. An electric glow discharge device as specified in claim 1 and havinga coating of an anti-glow material on the exterior surface of theportion of said inner electrode tube extending into said outer electrodetube from the said glass seal.

4. An electric glow discharge device as specified in claim 3 wherein thesaid anti-glow material is comprised of powdered aluminum.

5. An electric glow discharge device as specified in claim 1 wherein theinner wall of the said inner electrode tube is coated with barium oxide.

6. An electric glow discharge device as specified in claim 1 wherein thesaid electrode tubes are composed of an alloy consisting essentially ofiron, nickel, and cobalt.

7. An electric glow discharge device as specified in claim 1 wherein thesaid outer electrode tube is joined by said glass seal to a region ofthe said inner electrode tube between the ends thereof.

8. An electric glow discharge device as specified in claim 7 wherein thesaid inner electrode tube is hermetically sealed olf at its outer end bya tipped-off glass exhaust tube fusion-sealed thereto.

9. An electric glow discharge device as specified in claim 7 wherein thesaid inner electrode tube is hermetically sealed off at its outer end bya plug of fusible material therein consisting of a metal which will wetand adhere to the metal of said inner electrode tube.

References Cited UNITED STATES PATENTS 2,056,662 10/1936 Foulke 3l32l0 X2,465,084 3/ 1949 Greiner 313-318 X 2,556,059 6/1951 Braunsdorif 3l3318X 2,667,593 1/1954 Doolittle 3 133 18 X 2,802,130 8/1957 Engelman et a1.313--210 X 2,876,385 3/1959 Landrey 313-210 X 3,020,437 2/ 1962 Horan3133 l8 FOREIGN PATENTS 610,004 3/ 1935 Germany.

JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner US.Cl. X.R.

